Biogas, also referred to as bio-methane, swamp gas, landfill gas, and digester gas, is the product of anaerobic digestion, e.g., the decomposition of waste material without the presence of oxygen which yields predominantly methane and carbon dioxide. After proper processing to appropriate purity, captured biogas is usable as a green/renewable fuel or fuel for natural gas-powered vehicles/engines. One such system for multi-stage biogas treatment is detailed in U.S. Pat. No. 9,535,045, which describes a system to process biogas. The content of that patent is incorporated herein by reference.
Several generation and collection sources of biogas exist across a wide range of disciplines, i.e., waste water treatment, solid waste/land fill disposal and management, food processing plants, and the agricultural industry, including processing farm animal waste.
Before it can be used effectively as a fuel source, however, biogas must be processed. Such processing requires removal and/or minimization of typical impurities found in the biogas output stream. The cleaning begins with particulate removal, followed by removal of water, and, when the desired end product is intended to provide a high quality gas stream, H2S, sulfur species, siloxanes, CO2, digestion generated VOCs (Volatile Organic Chemicals) and oxygen. Subject to required purity/energy content standards, the resulting cleaned gas may be utilized as CNG (Compressed Natural Gas) for powering vehicles.
The purity requirements for use of processed biogas as Natural Gas Vehicle (NGV) fuel or compressed natural gas (CNG) are established by standards such as ISO 15404-2006. In addition to the above-mentioned scrubbing, that standard calls for the removal of all moisture for the gas to be compressed at high pressures, e.g., 6,000 psig. The success of such processing must again be confirmed through sample takeoff and analysis.
Particularly in the context of CNG, a need exists for a system and method assuring maintenance of a pre-established energy content from an obtained biogas stream and providing augmentation by blending of a refined gas with the biogas stream of when the content falls below the pre-established minimum combustion energy profile threshold.